Acoustic spark chamber



OC- 11, 1966 F. A. KlRsTx-:N ET AL 3,278,892

ACOUSTIC SPARK CHAMBER B Sheets-Sheet 1 Filed Nov. 4, 1963 FREDER/CK A. KIRSTEN BY BOGDAN C. MAGL/c ATTORNEY Oct. l1, 1966 F, A, KlRsTEN ET Al. 3,278,892

ACOUSTI C SPARK CHAMBER Filed NOV. 4, 1965 2 Sheets-Sheet 2 IN VEN TORS FREDER/CK A. K/RsTE/v By BOGDA/v C. MAGL/c United States Patent O 3,278,892 ACOUSTIC SPARK CHAMBER Frederick A. Kirsten, Lafayette, Calif., and Bogdan C.

Maglie, Geneva, Switzerland, assignors to the United States of America as represented by the United States Atomic Energy Commission Filed Nov. a, 1963, ser. No. 321,370 5 Claims. (Cl. 340-15) This application is a continuation-in-part of our c0- pending application Serial No. 277,968, tiled May 3, 1963, for Acoustic Spark Chamber and now abandoned.

The present invention relates to spark chamber devices for detecting charged particle trajectories and more particularly to a chamber having means for acoustically detecting the location of charged particle paths therein. The invention described herein was made in the course of, or under, Contract W7405-eng48 with the United States Atomic Energy Commission.

The conventional spark chamber consists essentially of a series of parallel plates within a gas-filled chamber. When a charged particle passes through the chamber and a charge is applied to the plates, the particle path is made visible by sparks occurring between the plates. The spark patterns are visible through the chamber windows and are customarily recorded by means of stereoscopic photographs.

The spark chamber has found increasing importance as a track detecting device in the study of the behavior of subatomic particles, as it inherently combines certain advantages found only separately in the cloud and bubble chamber. In particular, more selective timing and improved clarity in the photographic exposures is obtained. As is the case with these other instruments, however, the problem of handling, developing and scanning the rapidly accumulated quantities of photographic data is considerable. In general, such instruments have tended to produce nuclear data much faster than it can be analyzed with a practical investment in equipment and personnel.

Also inherent in the spark chamber however are characteristics which make other methods of track detection and recording plausible. The present invention provides a means for acoustically detecting the spark patterns by virtue of the shock waves produced thereby. Since the overall path is manifested in increments, i.e., by the sparks across the successive separate gaps in the chamber space, the sparks can be located acoustically within each separate gap. Computer operations on the acoustical information rapidly locate the sparks and reconstruct the particle paths. It can be seen that such a method completely circumvents the the cumbersome problems associated with the conventional photographic recording of such data.

The invention comprises a series of acoustic probes which extend through the spark chamber wall and terr minate at known locations within each gap between the chamber plates. The probes act as wave guides and transmit along their length the sonic waves produced upon the occurrence of a spark in the associated gap. An electro-acoustic transducer element contacts the opposite end of each probe and produces an electrical signal in response to pressure increases exerted on it by the probe. Each transducer output is coupled to a separate channel of a time comparison circuit wherein the timespans between the occurrence of the spark in the chamber and the arrival of the resulting sonic wave at each of the probe tips are determined.

Given these separate times of travel of the spark sound event to the separate probe tips and knowing the velocity of sound in the particular chamber medium, the distance of the sound travel to the separate probes can be determined. By virtue of the fact that more than one probe ICC is present in each gap, which probes are positioned at known co-ordinate locations therein with respect to the gap, the solution of simultaneous equations of these coordinate distances in a particular gap reveals the coordinate location of the spark center of that gap.

The mathematical operations are programmed into a computer whereby the spark locations for each gap are calculated directly from the probe output data and the particle paths through the chamber are re-constructed from the spark locations in the successive gaps.

It is accordingly an object of the present invention to facilitate the study of high-energy nuclear charged particles.

. successive plates.

It is another object of the invention to improve and implement spark chamber type charged particle detection.

It is a further object of this invention to provide a rapid and convenient means for locating and recording the path of charged particles within a spark chamber.

It is another object of this invention to provide a means for acoustically detecting charged particle paths in a spark chamber whereby the delay and effort required for photographic data detection may be avoided.

It is still another object of the invention to provide acoustic detection of charged particle paths in a spark chamber whereby the electronic form of the output information may be directly analyzed by a computer program.

The invention, both as to its organization and operation, together with further objects and advantages thereof, will be best understood with reference to the following specification taken in conjunction with the accompanying drawing, of which:

FIGURE l is a diagrammatic view of a spark chamber having acoustic particle track locating means incorporated therein and showing the electrical circuitry associated therewith, and

FIGURE 2 is a section view showing a portion of a spark chamber and the detailed structure of one of the acoustic probes shown diagranirnatically in FIGURE 1.

Referring now to the drawing and more particularly to FIGURE l thereof, there is shown a spark chamber 11. The spark chamber 11 comprises an air-tight rectangular housing 12 which encloses the chamber gas, typically argon or neon. A plurality of electrically conductive plates 13 are disposed within the housing 12. The plates 13 are rectangular in shape and are arranged within the chamber in parallel and spaced apart relationship whereby a series of equal width gaps 14 are formed between The outer plates of this arrangement and the alternate plates therebetween, indicated by primes in the drawing, are connected to a ground line 16 external to chamber housing 12. The remaining plates 13, intermediate to the grounded plates, are connected to a common output 17 of an external high voltage pulse generator 18, whereby an electric field may be established simultaneously in all of the gaps 14 upon occurrence of a pulse from the generator.

A broad flat charged particle detector 19 is disposed in the chamber 11 near the end thereof and transverse to the path of the incoming charged particles, indicated in the drawing `by arrow 21, and lhas an output coupled to a trigger input 22 of pulse generator 18. The counter 19 may be selectively adjusted to discriminate among the incoming particles to detect those having desired characteristics. Upon detecting an incoming particle of interest the counter 19 triggers an output pulse from the pulse generator 1-8 to apply a charge t-o the plates 13. In the presence of the electric field thereby established in the gaps 14, sparks -occur along the lines of ionized gas particles left by each passing charged particle. A Itypical example posed with respect to the spark chamber 11.

3 of such particle ionization trails is shown in FIGURE 1 by the broken lines 23, while the resulting sparks along these paths are indicated by the heavy solid lines 23 between the plates 13. The above described elements constitute -thesalient features of a conventional spark chamber in which it has heretofore Ibeen -the practice to record the position of particle tracks by means of a camera situated to one side of the chamber and viewing the gaps 14. While the data can be efliciently recorded by such means, the subsequent developing Iand analysis of the photos involves considerable e'Iort and delay. To avoid these problems, the present invention provides Ia novel acoustic track detecting `means which can `supply track position data directly to ra computer for immediate analysis.

-Referring still to FIGURE -1 there is shown a plurality of rod-shaped acoustic probes 24a to 2411 disposed in a bank along one wall of chamber 11 with one probe projecting into each of the gaps 14. At least one additional bank of similar probes 24a to 2411' is `attached to the chamber 11 and arranged with one probe projecting into each gap 14. In this Way at least two probes are inserted into each of the gaps and are positioned at known locations therein. The probes 24 in each gap 14 respond separately to any spark shock wave that is produced in that gap. The relative times of arrival of the shock waves to each of the separate probes in a particular gap thus enables the position of the spark from which the shock Wave emanated to 'be determined, as will hereinafter be more fully described.

Referring now to FIGURE 2 there is shown a detailed section view of one of the acoustic probes 24 las it is dis- The probe 24 comprises a slender glass (Pyrex) rod 26 which extends into Ithe chamber 11, through an opening 2-5 provided in the chamber wall 12, in .alignment with associated l gap `14. The rod 26 is positioned with its rounded detecting tip 2-7 located .a short distance within the gap 14 Where it is responsive to the shock waves therein. The

' rod 26 lacts as a sonic wave guide and transmits the shock along its length, out of the chamber, to -an electro-acoustic transducer 29 yat the other end of the rod 26. The transducer 29 may be a disc of barium-titanate, silver coated on both faces. The disc 29 is disposed coaXially with the rod 26 and is in .abutment with the at end thereof. For electrical conduction this end of rod 26 is provided -with -a platinum coating 31 and Iacoustic contact between the trod 26 and the disc face 29 is enhanced by a layer of apiezon grease 32 therebetween. The opposite face of the transducer disc 29 abuts the liat end surface of a large cylindrical lead damper 33. The damper 33 presents suicient inertial resistance Ito the system that the shock Wave transmitted by the wave guide 26 will result in the necessary compression of the transducer 29 whereby the mechanical energy is converted .to electrical energy therein. A rst electrode 34 is connected to platinum coating 31 of rod 26 and a second electrode 36 is connected to lead damper 33 to conduct the output pulses of transducer 2-9.

A portion of the length of the wave guide rod 26 external to the chamber 11 is enclosed in a Lucite sleeve 37. The rod 26 is supported in the sleeve 37 and spaced therefrom to provide acoustical isolation by rubber O-rings 38. A wide flange 39 at the end of sleeve 37 away from charnber 11 provides a connecting means for other elements of the probe housing. A tubular Lucte casing 41, larger than sleeve 37, tits over lead damper 33 and is ailixed at one end to tlange 39. A cut-out section 42 near this end of Ithe casing 41 provides access to the transducer electrodes 34 and 36. The damper 33 is spaced from the casing 41 by O-ring supports 43. The casing 41 extends beyond the end of the damper 33 and is internally threaded at this end to laccommodate la threaded alumi- The probe 24 is mounted on the exterior chamber l wall 12 by a threaded d .ucite collar plate 47 engaged in .48. The variable positioning of the lilange 39 is cornmunicated through sleeve 37 and O-rings 38 to the wave guide rod 26 yand thereby provid-es for minor adjustments of the wave guide position within the spark chamber gap 14. A stainless steel bellows 52 iiexibly encloses the sleeve 37 between collar plate 47 and flange 39.

Referring again to FIGURE ll, there is shown the timing and data transmission circuitry associated with the probes 24. The starting signal is tak-en from the pulse generator 18 which supplies the charge to the spark chamber plates 13. This signal, originating with the detection of ,a charged particle by detector 19, occurs simultaneously with the sparking and thus provides the initial time 'reference for measuring the shock wave travel.

The time reference signal from generator 18 to the counting circuitry is delayed in -a first time delay 53, which delay is of the one-shot type responding only to the leading edge of the incoming pulses thereto. 'Ilhis delay is provided to prevent premature energiZati-on of the subsequent circuitry due to electrical noise generated by the spark gap and the spark chamber. The time delay 53 -output is branched at junction 56 and is connected to a second time delay 57 and to first inputs 58 of a plurality of lbi-stable multivibrators 59a to 5911 associated with the output channels of probes 24a to 2411 respectively. The delayed reference signal energizes multivibrators 59, simultaneously triggering continuous outputs therefrom which are applied to lirst inputs 61 of a plurality of and type gating circuits 62a to 62n. A second input 63 -of the gate circuits 62 continuously receives clock pulses from a tWo-megacycle oscillator clock 63. The appearance of the multivibrator 59 signals as gate input 61 opens the gates 62 and transmits the clock pulses to a plurality of scalers 66a to 66H separately coupled to the outputs of gating circuits 62a to 6211. Thus the sealer 66 of each probe 24 ioutput channel simultaneously begins a count Vof the clock 63 pulses with the occurrence of the spark in the chamber gaps 14.

Each of the probe 24 outputs is connected through a separate pulse height discriminator 67 to a first input 68 of an associated one of a plurality of or type gate circuits 69a to 6911. A second input 71 of each gate 69 is coupled to the output of time delay 57. The gate 69 output of each channel supplies a second input 72 of the respective channel bi-stable multivibrator 59 and provides the triggering-olic pulse therefor. Thus, a shock wave signal from a probe 24 is transmitted by the or gate 69 to de-energize multivibrator 59. This cl-oses the and gate 62 and stops the count of clock 64 pulses in the channel Scaler 66. The count in the sealer 66 thus represents the acoustic time delay from the spark to the corresponding probe transducer 29.

Where the particle path does not enter a gap 14 and there occurs no spark therein there will be no transducer output lpulse to `de-energize the multivibrator 59 of that channel and stop the sealer `66 count. For this reason a reset pulse from second time delay 57 is delivered to each of the or gates 69 whereby those which have not received a transducer signal will transmit the reset signal to trigger ott the multivibrators 59. Since the count accumulated in the scalers 66 in such cases is greater than the longest possible acoustic delay in the chamber, such sealer output information is readily recognized as invalid.

The output of each channel lscaler 66 is connected to an information recording device 73 such as a print-out recorder or a magnetic-core buffer store. The reset pulse from time delay 57 supplies a read-out com-mand signal to the recorder 73 at input 74 thereof whereupon the counts contained in each scaler 66 are transferred thereto for storage Iand subsequent analytical computation by a suitable computer 78.

These counts contained in the scalers 66 and transferred to the recorder 73 for each spark event represent the number of oscillator 64 pulses received by the particular probe channel during the time interval between the delayed reference signal from first delay 53 and the arrival of the shock wave at the particular probe transducer 29. These counts thus correspond to a counted time of N/ f, where N is the number of pulses received and f is the pulse frequency of the oscillator clock 64.

In order to obtain the precise acoustic delay time T between the occurrence of the spark and the `arrival of the shock wave at the probe detecting tip 27 the sealer 66 counts must be corrected. A first correction must subtract the travel time of the sound wave :along the length of the wave guide rod 26 in order that the measured time be Ionly to the detecting tip 27 rather than to the transducer 29 of the probes 24. The amount of this correction is a unique constant for each probe channel and is dependent upon the length of the particular guide rod 26 of each probe 24. A second correction ladds to the counted time the artificial time delay introduced in the reference starting signal by time delay 53. This correction is a constant of the circuit and the same amount applies to all the probe 24 channels. The third correction arises from the physics of `shock wave behavior wherein in the immediate vic-inity of a spark the shock Wave velocity is several times greater than that of ordinary sound in the chamber medium. After a few centimeters of travel the wave velocity approaches the normal sound velocity C. The amount of this correction can be best determined experimentally by using a movable test spark in the gap 14 and measuring the sound travel time at varying spark distances from the probe tip 27. Extrapolating from this data to Zero distance will yield the correction time for this effect, which amount is then t0 be added to the counted time. Such correction is suf iiciently accurate that the wave travel may be assumed at 4a constant velocity provided only that the detecting tips 27 are located beyond the shock wave region of the sparks. For this reason, and as can be seen in FIGURE l, the area presented to the incoming particles 27 by the particle detector 19 is slightly smaller than the surface area of the conducting plates 13 and 13 in order to prevent sparking in the peripheral regions of the gaps 14 where the probe tips 27 are located.

Given the corrected time delays T between the spark and the shock wave arrival at two probe tips within an individual gap 14, the spark location within the gap can be determined. Let T1 and T2 represent the respective time delays of the two probes 24 and let C represent the established velocity of sound in the chamber gas. The spark coordinates x and y in the gap will be the point of intersection of two circles of radius R1=% and respectively, the centers of which circles are at the known coordinate location of the probe tips 27. If the probes are separated by a distance (a) along the assumed x-axis of the gap space, the spark center coordinates will follow the relationship:

Thus it can be seen that from the acoustic time delay data stored in recorder 73, subsequent computer operations can readily calculate the spark locations in e-ach gap 14 for each spark occurrence of the chamber 11, techniques for accomplishing this operation being apparent to those skilled in the art. From these locations the sposition and angle of the particle paths through the chamber 11 can be reconstructed by the computer program for analysis.

While the invention has been described with respect to a single embodiment thereof, it will be apparent to those skilled in the art that numerous variations and modifications may be made within the spirit and scope of the invention and it -is not intended to limit the invention except as dened in the following claims.

What is claimed is:

1. In a charged particle sensitive instrument of the class having a plurality of electrically charged plates spaced apart within a gas lled chamber to form a series of spark gaps and having a detector indicating the passage of a charged particle therethrough, a means for electronically detecting the location of charged particle paths through said chamber comprising:

(a) a plurality of sonic wave guides with at least two thereof extending into each spark gap of said chamber at spaced apart positions in said gap, said wave guides being responsive to shock waves emanating from sparks therein,

(b) a like plurality of acoustical-electrical transducer elements of the piezoelectric class each being disposed at the end of a separate one of said wave guides and producing an electrical signal in response to pressure exerted thereon by said wave guide,

(c) a like plurality of bi-stable multivibrators each receiving the signal from said detector at a rst input thereof and each having a second input coupled to the output of a separate one of said transducers, said multivibrators producing an output signal during the interval between said detector signal and said transducer signal,

(d) an oscillator,

(e) a plurality of coincidence gates each having a rst input connected to the output of a separate one of said multivibrators and having a second input coupled to said oscillator, said gates transmitting said oscillator pulses during the input coincidence of said multivibrator signal therewith,

(f) a like plurality of scalers each coupled to the output of a separate one of said coincidence gates and counting the oscillator pulses therefrom, which counts correspond to the acoustic time delays between the spark of the particle path in a gap and the sonic wave arrival at the positions of the wave guides disposed therein, and

(g) a recording means having a plurality of inputs separately coupled to said scalers and receiving said counts therefrom.

2. In a charged particle sensitive device of the class having a plurality of electrically charged parallel plates spaced apart within a gas filled chamber to form a series of spark gaps and having a detector indicating the passage of a charged particle therethrough, a means for electronically detecting the location of charged particle paths through said chamber comprising:

(a) a plurality of sonic wave guides with at least two thereof extending into each spark gap of said chamber at spaced apart positions in said gap, said wave guides being responsive to shock waves emanating from sparks therein,

(b) a like plurality of acoustical-electrical transducer elements each being disposed at the end of a separate one of said wave guides and producing an electrical signal in response to pressure exerted thereon by said wave guide,

(c) a like plurality of amplitude discriminator circuits each having an input coupled to the output of a separate one of said transducers and discriminating against low amplitude noise signals therefrom,

(d) a like plurality of bi-stable multivibrators each receiving the signal from said detector at a rst input thereof and each having a second input coupled to the output of a separate one of said discriminator circuits, said multivibrators generating an output signal during the interval between said detector signal and said discriminator signal,

(e) a high frequency clocking oscillator,

(f) a like plurality of `coincidence gates each having a iirst input connected to the output of a separate one of said multivibrators and having a second input coupled to said oscillator, said gates transmitting said oscillator pulses during the input coincidence of said multivibrator signal therewith,

(g) alike plurality of scalers each coupled to the output of a separate one of said coincidence gates and counting the oscillator pulses therefrom, which counts correspond to the acoustic time `delays between the spark of the particle path in a gap and the sonic wave arrival at the positions of the wave guides disposed therein, and

(h) an information storage device having a plurality of inputs coupled to said scalers and receiving said `counts therefrom.

3. In combination with a gas-filled parallel plate spark vchamber of the class having a series of spark gaps dened by said plates, an acoustical probe for detecting charged particle passages across the gaps thereof, said probe comprising a tubular enclosure disposed adjacent the side of a gap of said chamber and directed theretowards, a wave 'guide rod longitudinally disposed in said enclosure and having a rounded sensing end extending into said spark gap of said chamber and having a flat opposite end, a disctype piezoelectric transducer disposed against said at end of said rod in said enclosure, a heavy damper element secured against said transducer disc, said damper being disposed and resiliently supported in said enclosure, and electrical terminal means coupled to said transducer for conducting current pulses generated in said transducer by sonic pressure exerted thereon from said wave guide.

4. In a charged particle sensitive instrument of the class having a plurality of spaced apart parallel plates and having a pulse source for applying a potential difference between neighboring ones of said plates whereby a spark is produced by the passage of a charged particle across the gap between said neighboring ones of said plates, the combination comprising:

(a) a pair of acoustic-electric transducers associated with each of said gaps and situated outside thereof, said pair of transducers each having an associated acoustic wave detecting element in said gap at spaced apart locations therein, said acoustic wave detecting elements being sonic waveguide rods extending from said transducers into the outer regions of said gaps,

(b) a plurality of timing circuits a separate one being 8 coupled to each of said transducers and being coupled to said pulse source for determining the time intervals between the application of said potential difference to said plates and the detection of an acoustic wave by the associated transducer, and

(c) output means for transferring said time interval determinations to a computer for analysis whereby the .position of said sparks in said gap may be determined.

5. In a charged particle sensitive instrument of the class having a plurality of spaced apart parallel plates and having a pulse source for applying a potential difference between neighboring ones of said plates whereby a spark is produced by the passage of a charged particle across the gap between said neighboring ones of said plates, the vcombination comprising:

(a) a pair of acoustic-electric transducers associated with each of said gaps, said pair of transducers each having an associated acoustic wave detecting element in said gap at spaced apart locations therein,

(b) a plurality of timing circuits a separate one being coupled `to each of said transducers and being coupled to said pulse source for determining the time intervals between the application of said potential difference to said plates and the detection of an acoustic wave by the associated transducer,

(c) a particle detector disposed in the path of particles approaching said gap and connected to initiate operation of said pulse source and to initiate operation of said timing circuit upon detection of a charged particle,

(d) a reset signal source coupled to said timing circuits for cancelling the accumulated count thereof a predetermined interval after detection of a particle by said detector which interval exceeds the time required for said transducers to detect acoustic waves originating at the region of said gaps which is most remote from said transducers, and

(e) output means for transferring said time interval determinations to a computer for analysis whereby the position of said sparks in said gap may be determined.

References Cited by the Examiner UNITED STATES PATENTS 4/1962 Reifrel Z50- 83.1 3/1965 Douglas 340-16 

1. IN A CHARGED PARTICLE SENSITIVE INSTRUMENT OF THE CLASS HAVING A PLURALITY OF ELECTRICALLY CHARGED PLATES SPACED APART WITHIN A GAS FILLED CHAMBER TO FORM A SERIES OF SPARK GAPS AND HAVING A DETECTOR INDICATING THE PASSAGE OF A CHARGED PARTICLE THERETHROUGH, A MEANS FOR ELECTRONICALLY DETECTING THE LOCATION OF CHARGED PARTICLE PATHS THROUGH SAID CHAMBER COMPRISING: (A) A PLURALITY OF SONIC WAVE GUIDES WITH AT LEAST TWO THEREOF EXTENDING INTO EACH SPARK GAP OF SAID CHAMBER AT SPACED APART POSITIONS IN SAID GAP, SAID WAVE GUIDES BEING RESPONSIVE TO SHOCK WAVES EMANATING FROM SPARKS THEREIN, (B) A LIKE PLURALITY OF ACOUSTICAL-ELECTRICAL TRANSDUCER ELEMENTS OF THE PIEZOELECTRIC CLASS EACH BEING DISPOSED AT THE END OF A SEPARATE ONE OF SAID WAVE GUIDES AND PRODUCING AN ELECTRICAL SIGNAL IN RESPONSE TO PRESSURE EXERTED THEREON BY SAID WAVE GUIDE, (C) A LIKE PLURALITY OF BI-STABLE MULTIVIBRATORS EACH RECEIVING THE SIGNAL FROM SAID DETECTOR AT A FIRST INPUT THEREOF AND EACH HAVING A SECOND INPUT COUPLED TO THE OUTPUT OF A SEPARATE ONE OF SAID TRANSDUCERS, SAID MULTIVIBRATORS PRODUCING AN OUTPUT SIGNAL DURING THE INTERVAL BETWEEN SAID DETECTOR SIGNAL AND SAID TRANSDUCER SIGNAL, (D) AN OSCILLATOR, (E) A PLURALITY OF COINCIDENCE GATES EACH HAVING A FIRST INPUT CONNECTED TO THE OUTPUT OF A SEPARATE ONE OF SAID MULTIVIBRATORS AND HAVING A SECOND INPUT COUPLED TO SAID OSCILLATOR, SAID GATES TRANSMITTING SAID OSCILLATOR PULSES DURING THE INPUT COINCIDENCE OF SAID MULTIVIBRATOR SIGNAL THEREWITH, (F) A LIKE PLURALITY OF SCALERS EACH COUPLED TO THE OUTPUT OF A SEPARATE ONE OF SAID COINCIDENCE GATES AND COUNTING THE OSCILLATOR PULSES THEREFROM, WHICH COUNTS CORRESPOND TO THE ACOUSTIC TIME DELAYS BETWEEN THE SPARK OF THE PARTICLE PATH IN A GAP AND THE SONIC WAVE ARRIVAL AT THE POSITIONS OF THE WAVE GUIDES DISPOSED THEREIN, AND (G) A RECORDING MEANS HAVING A PLURALITY OF INPUTS SEPARATELY COUPLED TO SAID SCALERS AND RECEIVING SAID COUNTS THEREFROM. 